Earlier quoted context omitted.
You can replicate all calculations done by LLMs with pen and paper. It would take ages to calculate anything, but it's possible. I don't think that pen and paper will ever "think", regardless of how complex the calculations involved are.
You can simulate a human brain on pen and paper too.
That's an assumption, though. A plausible assumption, but still an assumption.
We know you can execute an LLM on pen and paper, because people built them and they're understood well enough that we could list the calculations you'd need to do. We don't know enough about the human brain to create a similar list, so I don't think you can reasonably make a stronger statement than "you could probably simulate..." without getting ahead of yourself.